In existing plasticising machines a single plasticising chamber containing a screw piston is used to feed an outlet to a moulding machine. The rate at which mouldings can be produced is determined by the rate at which the plasticising chamber can process material during the time when the moulding function of the machine is not operative. To overcome the delay in the production of mouldings it is desirable that the plasticising function can proceed at the same time as the moulding function. The plasticising machine may be arranged to perform an extrusion function in which case it is desirable to be able to carry out continuous extrusions without waiting for a plasticising function to take place between successive strokes of the piston.
The invention relates to plasticising apparatus and to a method of plasticising plastics material.
The invention provides apparatus for producing a flow of plasticised plastics material comprising at least two chambers connected in parallel to a common outlet, means associated with each chamber to plasticise material in that chamber, means to force plasticised material from each of the chambers to the outlet, means being provided to isolate each of the respective chambers from the outlet.
In one form of the invention the isolation means is such that only one chamber may be in communication with the outlet at one time.
In an alternate form of the invention the isolation means is such that both of the chambers may be in communication with the outlet at the same time.
The invention includes apparatus as described above in combination with an injection moulding machine in which the outlet of the apparatus is arranged to feed a mould or moulds in the injection moulding machine.
The invention also includes apparatus as described above in combination with a blow moulding machine, in which the outlet of the apparatus is arranged to feed a mould or moulds in the blow moulding machine.
The invention also includes apparatus as described above in combination with an extrusion die, and arranged to operate as an extrusion machine.
The invention also provides a method of providing a flow of plasticised plastics material which comprises the steps of plasticising material in at least two separate chambers, connecting the chambers to a common outlet and forcing the plasticised material to the outlet from one of the chambers while refilling another or the other chamber with material and plasticising the material in the chamber.
Preferably the plastics material is forced into a mould after leaving the outlet, and the mould is filled completely by material from only one chamber.
In this form a second mould may be completely filled by material from a second chamber while said one chamber is being refilled with, and is plasticising, further material.
In an alternative form of the invention the plastics material is forced into a mould after leaving the outlet, and the contents (or part of the contents) of more than one chamber are used to fill the mould.
In this last mentioned form it is preferred that a first chamber is connected to fill part of the mould, and is then disconnected from the mould, and then a second chamber is connected to fill another part of the mould.
Alternatively a first chamber is connected to fill a part of the mould, and a second chamber is connected to the mould to fill another part of the mould before the first chamber is disconnected from the mould.
The first chamber may be used more than once to fill the mould.
In another embodiment the chambers may be connected to the outlet serially, i.e. without interruption of the flow.